We plan to pursue our studies of cardiovascular pathology along several lines, as follows: (1) Electron microscopic sampling of rat aortas after injection of vasoactive substances such as histamine, bradykinin, and angiotensin, in order to confirm or disprove the notion of endothelal contraction in this model. (2) Study of the effect of total, transient or permanent occlusion in large arteries and veins in the rat and in the dog. (3) Electron microscopic study of the pathogenesis of aneurysms after surgical repair with glue in the carotid artery of the rat. (4) Further electron microscopic study of the effect of spasm on the arterial wall, including the effect of repeated episodes of spasm. (5) Electron microscopic study of the effect of pulmonary embolism on the myocardium of the rat (microspheres will be used for producing widespread embolization). Similar studies will be conducted in the dog, with simultaneous measurements of cardiovascular function. (6) Electron microscopy of early thrombosis and repair, induced in the dog pulmonary artery with an inflatable cuff. (7) Electron microscopic studies of the "normal" arterial wall, including the microanatomy of its elastic structures, and the effects of aging. BIBLIOGRAPHIC REFERENCES: Cuenoud, H., Majno, G., and Joris, I.: Myocardial effects of pulmonary microembolism: A light and electron microscopic study in the rat. Fed. Proc. 36: (3) 572, 1977. Joris, I., and Majno, G.: Cell-to-cell herniae in the vascular wall. An electron microscopic study. Am. J. Path. 86: May, 1977 (in press).